Figure 2.
Nucleosome organization. Each nucleosome is composed of an octamer comprising four histones proteins, i.e., H2A, H2B, H3 and H4, wrapped twice by the DNA molecule. Methyl groups (CH3) can be added or removed from the lysine (K) and arginine (R) residues of histone H3 and H4 in a nucleosome. Histone modifications, including methylation and acetylation, are important mechanisms for gene transcription regulation independent of the promoter methylation status. P, proline; S, serine; T, threonine. DNA molecule represented in red.